1. Field of the Invention
This invention relates to personal access control systems in general and, in particular, to a method and an apparatus for identifying an individual through a combination of speech and face recognition.
2. Description of the Prior Art
Speech recognition methods and apparatus have been used extensively in personal access control systems to limit access to secure facilities and to prevent the unauthorized use of information input and output devices of computers and various other machines. These systems analyze voice input signals to determine the identity or non-identity of an individual who is seeking access to the facility or use of the device.
In a typical system of this type, the individual seeking access or use is requested to utter a particular key word from among a sequence of predefined key words. The utterance of the key word is detected and analyzed by the speech recognition apparatus. The detected voice signature of the uttered key word is compared to a predetermined stored voice signature corresponding to the utterance of the same key word by a previously cleared known individual. Access is permitted when the compared voice signatures of the uttered key word and the stored key word are sufficiently similar to indicate identity of the individual seeking access with the known individual. An example of such a speech recognition system is described in U.S. Pat. No. 4,239,936, entitled "Speech Recognition System", which issued Dec. 16, 1980.
Personal identification using such speech recognition systems can be sufficiently accurate and reliable only if an indefinite computing time is available in which to analyze the uttered key word. But to avoid unacceptable waiting time, in practice the recognition process must be completed within a period of time of about three seconds or so from the initial request for access. For this shortened operation time, personal access control using speech recognition alone is subjected to identification error (the wrong individual is cleared or the right individual is not cleared) and falsification (voice impression, tape recordings, etc.). Further, because of the difficulty of detecting the beginning and duration of speech signals corresponding to utterance of the key word, current speech recognition systems must use highly sophisticated technology, including costly speech signal duration detecting units. Moreover, it has been found that an increase in technical effort to achieve higher speech recognition system accuracy does not produce a proportional increase in the detection accuracy.
Personal access control systems have also been implemented using visual recognition for identification of individuals. Visual recognition systems use characteristic portions of the human body for identification purposes. Typical of this type of access control are fingerprint recognition systems and facial feature recognition systems. One such system is described in U.S. Pat. No. 4,109,237, entitled "Apparatus and Method for Identifying Individuals through the Retinal Vasculature Patterns", issued Aug. 22, 1978. This latter system uses a method of scanning the individual's eye with a light source arranged in a selected pattern and detecting that portion of the light source pattern which is reflected from the person's retina, thereby locating each intercept of the light source pattern with a blood vessel. The intercept pattern thus obtained is then compared with stored intercept patterns previously obtained from individuals who are cleared for access. Personal access control systems using visual recognition alone demand an even higher level of technical effort and sophistication than acoustical recognition systems.